1. Preheat oven to 350 degrees. Grease a 9×13-inch baking pan2. In a medium bowl, mix together the flour, cinnamon, baking powder, baking soda and salt.3. In a large mixing bowl (I used my kitchen aid mixer), mix together the pumpkin, sugar, oil and eggs until smooth and thoroughly combined. Slowly pour in the flour mixture and mix until incorporated.4. Pour into the prepared baking dish.5. Bake for 30 minutes or until a thin knife inserted into the center comes out clean. Remove from the oven and cool completely before frosting.6. To make the frosting, cream together the butter and cream cheese until smooth. Add the powdered sugar. Mix in the vanilla extract.7. Pipe the frosting onto the cooled cake. Cut into squares and serve!